Current methods of forming contact and via level metalization using tungsten plug or via fill processes require that the film be deposited in several steps so that good contact/via resistance with reliable film properties are achieved. These steps typically include:
1. Depositing a titanium film to form titanium-silicide and promote good contact resistance between the silicon substrate and the tungsten plug; PA1 2. Depositing a titanium nitride barrier layer so that fluorine liberated in the tungsten deposition step does not etch the existing titanium underlayer; and PA1 3. Depositing a tungsten layer, including a plug, followed by etch-back or chemical mechanical polishing of the tungsten layer. Chemical mechanical polishing is a sacrificial-resist etch-back process which can rapidly remove a layer of film using a buffing wheel in connection with an abrasive slurry and a chemical etchant.
Previously, titanium and titanium nitride typically have been deposited using physical vapor deposition (PVD) methods such as sputtering. Using PVD, thick films of Ti and TiN must be deposited on the top layers of the device in order to achieve adequate bottom coverage.
While sputtering provides deposition of a titanium film at a low temperature, sputtering processes have various drawbacks. Sputtering normally yields very poor step coverage. Step coverage is defined as the ratio of film thickness on the bottom of a contact on a substrate wafer to the film thickness on the sides of the contact or the top surface of the substrate. Consequently, to sputter deposit a predetermined amount of titanium at the bottom of a contact or via, a larger amount of the sputtered titanium must be deposited on the top surface of the substrate or the sides of the contact. For example, in order to deposit a 200 .ANG. film at the bottom of a contact using sputtering, a 600 .ANG. to 1,000 .ANG. film layer may have to be deposited onto the top surface of the substrate or the sides of the contact. Since the excess titanium has to be etched away, sputtering is wasteful and costly when depositing titanium layers.
The step coverage of the contact with sputtering techniques decreases as the aspect ratio of the contact or via increases. The aspect ratio of a contact is defined as the ratio of contact depth to the width of the contact. Therefore, a thicker sputtered film must be deposited on the top or sides of a contact that is narrow and deep (high aspect ratio) in order to obtain a particular film thickness at the bottom of the contact than would be necessary with a shallow and wide contact (low aspect ratio). For smaller device dimensions in an IC, high aspect ratio contacts and vias are used and sputtering is inefficient and wasteful. The decreased step coverage during sputter deposition over smaller devices results in an increased amount of titanium that must be deposited, thus increasing the amount of titanium applied and later etched away. This increases the titanium deposition time, and the etching time that is necessary to remove excess titanium. Accordingly, as IC device geometries continue to shrink and aspect ratios increase, deposition of titanium-containing layers by sputtering becomes very costly.
Sputter deposition also requires the utilization of a separate reaction chamber. In applications where a first film is deposited by chemical vapor deposition (CVD), which is the preferred method, followed by sputter deposition of a second film, two different chambers are required. This may be followed by a third deposition process, such as sputter deposition in a third chamber. It is preferable to minimize the transport of the substrate from one reaction chamber to another and to conduct as many reactions as possible in a single chamber.
As shown in FIGS. 2A-2D, silicon substrate 110 with oxide layer 112 and via or plug 114 are provided. Titanium layer 116, having a thickness of approximately 600 .ANG., is then deposited by PVD. The PVD-Ti deposition results in Ti "overhang" 116a. Titanium nitride barrier layer 118, having a thickness of approximately 1,200 .ANG., is then deposited by PVD. The PVD-TiN builds upon Ti overhang 116a to form overhang 118a. Due to the poor step coverage of PVD-TiN, the area 118b under overhang 118a is thin and weak. This weakness results in failure of the TiN barrier layer during deposition of the tungsten plug. The source gas for tungsten layer 120 is tungsten hexafluoride (WF.sub.6). During deposition of the tungsten layer 120, fluorine gas is liberated. The fluorine gas is highly reactive with Ti layer 116 found under the TiN barrier layer 118. The reaction of F with Ti layer 116 at area 118b leads to liftoff 122 of the entire film stack. This liftoff 122 is known as a "tungsten volcano" due to the appearance of the failed stack.
It is frequently desired to deposit a film of titanium nitride over a film of titanium. The common method of depositing this film stack is sputtering. CVD Ti and TiN has been offered as a cost-effective alternative to sputtering. Application Ser. No. 08/401,859 (herein incorporated by reference in its entirety), filed Mar. 10, 1995, entitled "Plasma Enhanced Chemical Vapor Deposition of Titanium Nitride Using Ammonia" discloses PE-CVD of titanium nitride using titanium tetrachloride and ammonia. This, however, does not disclose formation of titanium and titanium nitride in a single reaction chamber, but specifically discloses withdrawing the substrate containing the titanium in between formation of the titanium and the titanium nitride films.
There is significant cost associated with each individual process that decreases the throughput of the machine. This includes the time to heat a wafer, stabilize the reaction chamber pressure and gas flows, and stabilize rotation. Each time a wafer enters a module, it must go through all these steps.
Transferring the wafer from station to station causes a time delay between the deposition of the titanium and subsequent nitridation and deposition of the titanium nitride film. During this time, the titanium film will undergo oxidation which can degrade the electrical properties of the film.
Therefore, it is one object of the present invention to provide a TiN barrier layer having no inherent weaknesses. It is another object of the present invention to deposit W plugs without the formation of tungsten volcanos. It is yet another object of the present invention to fabricate a TiN barrier from a Ti layer on a substrate in a single reaction chamber.